Image forming apparatus

Abstract

An image forming apparatus includes: an image forming section; a fixing portion; a discharging portion; a sheet transport passage including a curved portion and connecting between the fixing portion and the discharging portion; a reverse transport passage formed by branching off the curved portion; a transport roller pair rotatable in normal and reverse directions; a fixed guide portion provided on an inner corner side of the curved portion; and a swingable guide portion supported to be swingable. The swingable guide portion is arranged selectively either in a first position where it protrudes farther into the sheet transport passage than a guide rib formed on a transport surface of the fixed guide portion or a second position where its protruding height from the transport surface is equal to a height of the guide rib or where the swingable guide portion is retracted farther toward the transport surface than the guide rib.

What is claimed is: 
     
         1 . An image forming apparatus comprising:
 an image forming section forming an image on a sheet;   a fixing portion fusing the image formed by the image forming section on the sheet;   a discharging portion discharging the sheet having the image fused thereto by the fixing portion;   a sheet transport passage including a curved portion, the sheet transport passage connecting between the fixing portion and the discharging portion;   a reverse transport passage formed by branching off the curved portion of the sheet transport passage, the reverse transport passage being connected to an upstream-side part of the image forming section;   a transport roller pair provided in the sheet transport passage so as to be rotatable in normal and reverse directions, the transport roller pair transporting the sheet transported from the fixing portion by the normal rotation toward the discharging portion, the transport roller pair transporting, by switching back, the sheet transported to the discharging portion by the reverse rotation toward the reverse transport passage;   a fixed guide portion provided on an inner corner side of the curved portion of the sheet transport passage off which the reverse transport passage branches; and   a swingable guide portion supported so as to be swingable in a direction protruding out of or retracting into the fixed guide portion,   wherein   the image forming apparatus has a double-sided printing function whereby a sheet is, starting with a tail end thereof, guided into the reverse transport passage by the reverse rotation of the transport roller pair and then the sheet is, with obverse and reverse sides reversed, transported again to the image forming section, and   the swingable guide portion is arranged selectively either in a first position where the swingable guide protrudes farther into the sheet transport passage than a guide rib formed on a transport surface of the fixed guide portion or a second position where a protruding height of the swingable guide portion from the transport surface is equal to a height of the guide rib or where the swingable guide portion is retracted farther toward the transport surface than the guide rib.   
     
     
         2 . The image forming apparatus of  claim 1 ,
 wherein without applying of an external force, the swingable guide portion is arranged in the first position so as to be movable to the second position when a sheet passes through the curved portion.   
     
     
         3 . The image forming apparatus of  claim 2 ,
 wherein the swingable guide portion is arranged so as to occur a rotational moment that makes the swingable guide portion swing toward the first position, and   when a magnitude of an external force that acts on the swingable guide portion from a sheet passing through the curved portion exceeds a magnitude of the moment, the swingable guide portion moves to the second position.   
     
     
         4 . The image forming apparatus of  claim 3 ,
 wherein the swingable guide portion moves from the first position to the second position by being contacted by a head end part of a sheet passing from the sheet transport passage via the curved portion toward the discharging portion,   when a tail end of the sheet passing toward the discharging portion is located in the curved portion, during double-sided printing in which the transport roller pair is rotated in a reverse direction so that the sheet is transported in an opposite direction to permit the sheet to be guided, starting with a tail end thereof, into the reverse transport passage and then transported, with obverse and reverse sides reversed, again to the image forming section,   in a case where the sheet has a predetermined thickness or less, the swingable guide portion swings from the second position to the first position against an external force acting on the swingable guide portion from the tail end part of the sheet, and the sheet is guided into the reverse transport passage along the first transport guide, and   in a case where the sheet has more than the predetermined thickness, the swingable guide portion is held in the second position by an external force acting on the first transport guide from the tail end part of the sheet, and the sheet is guided into the reverse transport passage along the guide rib.   
     
     
         5 . The image forming apparatus of  claim 1 ,
 wherein when the swingable guide portion is located in the second position, at least an upstream-side part of the swingable guide portion in a reverse transport direction in which a sheet passes from the sheet transport passage through the curved portion toward the reverse transport passage is retracted farther toward the transport surface than the fixed guide portion.   
     
     
         6 . The image forming apparatus of  claim 1 ,
 wherein the swingable guide portion comprises a plurality of swingable guides arranged one at each of a plurality of positions corresponding to both end parts of a plurality of sizes in a sheet width direction.   
     
     
         7 . The image forming apparatus of  claim 6 ,
 wherein the fixed guide portion comprises a plurality of fixed guides arranged outward of each outermost one of the swingable guides in the sheet width direction and arranged between adjacent ones of the swingable guides in the sheet width direction.   
     
     
         8 . The image forming apparatus of  claim 7 ,
 wherein the fixed guides have each formed thereon a transport rib which extends in the sheet transport direction, and at least one of the fixed guides has formed thereon, close to a swingable guide, the guide rib parallel to, and with a larger protruding height than, the transport rib.